1. Field of the Invention
The present invention generally relates to a camera module. More particularly, the present invention relates to a camera module having an image sensor, which is capable of capturing moving pictures.
2. Description of the Related Art
Digital cameras taking the form of a camera module with an image sensor have recently become popular. Modularized digital cameras of a small size are under development as are applications to be built into portable communication terminals or portable digital devices, such as mobile phones.
Such a camera module includes a lens system with a plurality of lenses and an image sensor for electronically converting an image of an object formed upon it by the lens system.
The lens system may have, for example, an object lens facing an object, an aberration correction lens for suppressing aberration, and/or lenses for capturing an image of the object on the image sensor.
The optical performance of the lens system can be represented as an F-number. The F-number quantitatively defines light intensity that the lens can receive, expressed as
                    F        =                  f          D                                    (        1        )            where F (i.e. F-number) is the focal length f of the lens system divided by the diameter D of the lens system. As F is smaller, the lens system receives a larger light intensity. For example, given a lens system with F=2 and another lens system with F=2.8, the former is brighter than the latter under the identical conditions.
For video, with more frames per second, more natural moving pictures are achieved. This is possible by use of a software program. However, as additional frames per second are added, this increases noise in the moving pictures. Noise can be reduced by receiving more light. Therefore, it is preferable to take moving pictures using a lens system capable of receiving more light.
Meanwhile, still images can be captured even in the darkness if the F-number is small. However, an aberration may increase which causes degradation of image quality in a general photographing environment.
A typical digital camera module is equipped with a function for capturing both moving pictures and still images. However, the difference in photography between a moving picture and a still image leads to the degradation of either the quality of the still image or the moving picture.
That is, a camera module built in a general portable digital device is limited in the number of lenses forming a lens system due to limitations in size. The F-number for taking a still image ranges from 2.6 to 2.8. This F-number may cause a low light environment for moving pictures. As a consequence, the moving pictures are interrupted or noisier.